Remote control system



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L. v. LEWIS REMOTE com'non SYSTEM Filed se t. 2. 1944 2 Sheets-Sheet 2 Seeozzd Ee veateP ycafz'ozz INVENTdR [Zoyd Vi [65055; @i 1/ H13 ATTORNEY Patented Oct. 8, 1946 REMOTE CONTROL QYSTEM Lloyd V. Lewis, Pittsburgh, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application September 2, 1944, Serial No. 552,504

12 Claims.

My invention relates to remote control systems, and more particularly, to centralized traific control systems for railroads of the code type, and to the line or communication circuits for such systems.

Systems of this character, as illustrated, for example, by the remote control system of my United States Patent No. 2,229,249, issued January 21, 1941, employ a single communication channel, comprising a pair of line wires extending from the office through each station in turn, over which control codes are transmitted at times in one direction, from the ofiice to the stations,

while at other times indication codes are transmitted over the same channel in the opposite direction from the stations to the oflice, each transmitter having access to the line only when it is free. To prevent interference in the event transmission is started in both directions at the same time, the first step of each control code delivered by the transmitter at the office is made relatively long in comparison with the first step of an indication code delivered by a transmitter at a field station. When the transmitter at the ofiice and at a field station both start to transmit at the same time, the long element delivered by the office transmitter overrules the short element delivered by the station transmitter and suspends its operation until the code delivered by the office transmitter is completed, so that the two codes are transmitted successively without interference.

One object of my invention is the provision of a two-way repeater for use in systems of I this character, for repeating the code signals from one line circuit or channel to another. in either direction, which functions in such a manner that the direction of transmission through the repeater is determined in accordance with the character of the first step of the received code.

A further object is the provision of a two-way repeater for use in remote control systems in which the central ofiice operator is able to reverse the direction of transmission to break the transmission of a code from a remote station.

The purpose of my invention is to permit the line to be divided into sections energized by different sources of current so as to enable the distance between the office and the stations to beextended or to enable currents of different character to be used for energizing diiferent sec- 7 nectin the stations in systems of the character described, which channel may if desired employ the same carrier freouency for the transmission of codes in both directions.

I shall describe several forms of apparatus embodying my invention, and shall then point out the novel features thereof in claims.

Referring to the accompanying drawings, Fig. 1 illustrates a normally energized series connected line circuit system similar to that shown in my Patent No. 2 229.249, but which as shown herein is divided into two sections comprising the line circuits 1 and 2, respectively, connected by a repeater station including the apparatus of my invention.

Fig. 2 shows an alternative arrangement comprising a multiple connected line circuit system like that shown in the system of my Patent No. 2.259.573. issued October 21, 1941, for remote control systems, which is likewise divided into two sections comprising the line circuits 3 and 4 connected by a repeater station as in Fig. 1. In this view the codes are transmitted over line 3 by carrier currents employing the same frequency for transmission in both directions.

Fig. 3 shows a modification of the system of Fig. 2 in which the line circuit system is divided into three sections, one of which employs carrier current apparatus as in Fig. 2 but uses radio'in place of line wires. In this View the codes are transmitted between lines 3 and 4 as radio signals employing the same carrier frequency fo transmission in both directions. Fig. 4 shows a modification of the circuit for a selector reply 2F of the ofiice coding unit of Patent No. 2,229,249. for use in connection with the repeater of my invention.

Similar reference characters refer to similar parts in each of the views.

The repeater apparatus shown herein is generally similar in the different views. and it will be described in detail in connection with Fig. 1. In this view-it is to be understood that the terminal apparatus is that of the remote control'system of my Patent No. 2,229 249, only those portionsof the system which are directly associated with the line being shown herein. These portions include, at each field station, a master relay M, which when energized places the station apparatus in the transmitting condition, a transmitter relay T which operates periodically when relay M is energized to deliver its code to the line circuit, a line relay R responsive to the codes supplied to the line, and a coding unit CU comprising selecting pparatus for decoding the received codes and which also controls the operation of the associated transmitter relay T. The apparatus at the control oifice is generally similar to that at the stations,.comprising a master relay OM, a transmitter relay OT and a line relay OR governing a coding unit CU. In addition, a push button PB is provided by which relay OT may. besteadily energized for the purpose of breaking the transcomprising a timing relay L which serves like.

relay LI of Patent No. 2,229,249 to distinguish between the short or long character of the first step 'of a code, and two bridging relays ILB and 2L3 by means of which the direction'of transmission through the repeater'is established and which serve to make the repeater operation dependent upon the continued operation of the line relays 'When the code system is in its normal at rest condition, as shown, the line relays OR and RI are energized over line I and front contact b oi relay RZ, by battery BI at the ofiice, and the line relays R2 and R are energized o v e r line 2, back contact 0 of relay 2LB and front contact b of relay RI, by another battery B2 at the repeater station, so that the repeater is normally in condition to transmit signals in either direction.

The transmission of a code is initiated either by energizing relay OM at the ofifice to cause relay CT to periodically interrupt line I, o by energizing relay M at a field station to cause the associated relay T to periodically interrupt line 2'. In either case the opening of one lineopens the other and relays RI and R2 both release. Relay RI then completes a circuit irom one terminal- B of a suitable local source of current at its back contact a over back contact a of relay ILB through relay n to the other terminal o of the local source, so that relay L picks up, coin; pleting a circuit from terminal B over contacts a of relays RI and L through relay ILB to terminalC so that relay ILB picks up. By closing its contact b, relay ILB bridges contactb of relay R2, which serves when relay T is the initiating transmitter to advance the code in line I to the second step, providedirelay GT is 'not'operated, but when relay OT is the initiating transmitter the operation of may ILB serves to prevent transmission from line 2 to line I ,"thereby establishing one-way transmission through the repeater from line I to line 2, as required for the transmission of control codes by the offic relay OT.

When relay ILB picks up, the opening of its back contact a deenergizes relay L.

If the code is one initiated by relay OT; the first step delivered-to line I and repeated by relay RI into line 2 is a long step, and relay L releases before the second step of the code is reached; Relay RI responds to thecode operation of relay OT and its contact b repeats the code received from line I into line 2 tooperate relay R at each station in accordance with the operation of relay OT, the station coding units being conditioned by the first long stepto receive the remainder of the control code as explained in the patent. At the repeater station relay 2LB remains released, and relay: ILB 'is held picked up due to its intermittent energization over its own front contact a by relay RI on the odd-numbered code steps, and releases when relay RI becomes steadily encrgized at the end of the code, thereby restoring the repeater to its normal condition as shown,

If the code is an indication code initiated by relay T, and: relay OT is not operated, the first code step as repeated into line I is terminated as soon as relay I LB picks up and closes its front contact b, and consequently is somewhat shorter than the first step as measured by relay T. Relays RI and- OR become energized in response to the closing of contact b of relay ILB, and the closing of front contact b of relay RI connects batteryBZ- to. line 2; so that relays R2 and R pick up when relay T releases to begin the second step of the code. Since the first step delivered by relay T is relatively short, in comparison with the first step of a control code, relay R2 picks up beifor relay L releases, and completes a circuit from terminal B over front contacts a of. relays RI and R2 and contact b oi relay L through relay 2L}; to terminal 0. Relay 2L3 therefore picks up on the second step of an indication code, whereupon its contact b opens the circuit shunting contact I) of relay R2 to render relay R2 effective to control line I, and the operation of contacts 0 and d of relay ZLB renders relay RI inefiective to control line 2. Thus relay 2LB reverses the direction of transmission through the repeater to allow relay R2 to rep-eat the code received from line 2 into line I to operate relay OR at the oflice in accordance with the operation of relay T at the transmitting station. During the transmission of the indication code, relay ILB is held picked up by intermittent energization on the odd-numbered steps as already described and relay 2LB is held picked up over its own front contact a and contact 0 of relay I LB by intermittent energization on the even-numbered steps until relay RI becomes steadily energized at the end of the code.

It is to be understood that in the system of the patent the initiation of a control code by relay OT is dependent upon the energization of the master relay OM, and that relay QM cannot become energized while an indication code is being received at the ofiice. A control code thus takes precedence over an indication code initiated at about the same time only if relay OM picks up, otherwise the indication code is transmitted first. The direction of transmission is therefore determined by relay OM, that is to say, it is determined positively by the position of a sin l relay located at the office. It will be clear therefore that a single line repeater of the types ordinarily used in telegraph circuits would not be suitable for use in the system because in such repeaters the direction is determined by conditions at the repeater station.

Taking into account the time lag in the transmission of impulses over an electrically long line, it will be seen that in Fig 1, after the station transmitter relay T operates to initiate a code, a short time may elapse before its effect becomes manifest at the ofiice during which relays OM and OT may become energized. If relay OT becomes energized during the transmission of the first step of an indication code by relay T, relay RI remains released holding line 2 open after relay T releases to cause relay R to respond to the long step and conditioning the station coding unit to receive the code delivered by relay OT, thereby preventing the further operation of relay T until the code delivered by relay OT is completed, precisely as if the oflice and station were controlled over the same physical line circuit as shown in the patent. It will be clear therefore that the direction of transmission under this condition is determined, not by the relative order of arrival of signals from two directions at the repeater station, but by the position of the office relay OM, the same as when a repeater is not used.

In systems of the character described it is the practice to provide apparatus at each field station which is controllable from the omce by which the operator can disable the transmitter at a field station to prevent its continued operation in case of a fault. This is accomplished by holding the line relay R steadily released for a relatively long time interval by the operation of a push button PB located at the oifice. By reference to Fig. lit will be seen that if button PB is operated during the transmission of an indication code by relay T, relay OT will be steadily energized opening line I and causing the response of relay Rl to the code operation of relay R2 to cease, relay RI- remaining released and releasing relay 2L3, which places line 2 again under the control of relay Rl, causing relay R to remain released, as required. It will be seen that since the operator is able to reverse the direction of transmission through the repeater at will the distant line 2 is at all times controllable from the office.

It may also happen in the normal operation of the system that two station initiate indication codes at the same time. In this case the operation of relay M at the station nearer the oilice opens the portion of the line circuit leading to the more remote station so as to cause the two stations to transmit their codes successively without interference in the manner pointed out in the patent. In Fig. 1, some of the stations may be located in line i and others in line 2, and in this case if a station in line I and one in line 2 initiate codes at the same time relay M at the station in line I disconnects battery B! from relay R! and the effect at the repeater station is the same as when button PB is operated. It follows that the transmitter at the more remote station is disabled for the duration of the code transmitted by the nearer station with the same effect as if both stations were located in the same line section.

In the system of my patent the normal rate of operation is such that the short code steps have a duration of about .08 second, with the exception of the first step of an indication code which is about .05 second longer than the other short steps due to the operation of additional relays on that step. In the operation of the repeater as described this first step as received by the ofiice relay OR is shorter than the first step delivered by relay T, as already pointed out, so that step two as received at the office is lengthened by a corresponding amount and the margin against the improper operation of the corresponding selecting relay when the second step transmitted by relay T is short is decreased. By reference to the patent it will be seen that but one selecting relay is involved, namely relay 2F. The circuit for this relay, as shown. on Figs. 1. and 2 of the patent, and in a modified form in Fig. 4 of the present application includes contact e of a timing relay 01.2 and wire I35, which circuit is closed upon the release of relay 0L2 when the second step of an indication code is a long step. In Fig. 4 I have included a contact (1 of the re peating relay OLP of the patent, the release of which follows that of relay 0L2, in the circuit for relay 2F, whereby the effect of the increased length of the second step due to the repeater is overcome and the normal margin against operation restored. Relay 2F is also responsive to the second long step of a control code, but in that case its circuit already includes a contact I) of relay OLP, shown in Fig. 1 of the patent and the modification shown herein in Fig. 4 consequently does not change the operation of relay 2F in response to a control code. 7

Referring now to Fig. 2, in this view the coding apparatus is connected in multiple with the line wires instead of in series as in Fig. 1, the line circuit comprising two sections 3 and 4 connected by a repeater which is similar to that of Fig. 1 except as modified to correspond with the change in line conditions. In Fig. 2 the terminal apparatus is correspondingly modified and it is to be understood that in this view and in Fig. 3 as well, the remote control system is arranged as shown in my United States Patent No. 2,259,573, issued October 21, 1941. The line circuits of Fig. 2 are normally deenergized and the code in pulses are in consequence opposite in phase to those of Fig. 1. Line 4, to which the field stations are connected, is energized on the odd-numbered code steps only by a battery B4 at the repeater station in the case of control codes or by a battery B40. at the transmitting station in the case of indication codes, and is deenergized on the evennumbered code steps. Line 3 as shown is energized by carrier currents, that is to say, by alternating current codes generated by electronic'oscillators OSC at the ofiice and repeater stations, with electronic amplifiers and a frequency selecr tive filter HP interposed in the connections of the oscillators and of the line relays to the line. The repeater of my invention is of particular advantage in connection with carrier current transmission since it makes it possible to use currents of the same frequency for both directions of transmission and both oscillators are therefore preferably arranged to deliver currents of approximately the same frequency.

In Fig. 2 an impedance H3 is interposed in the connection of each line relay to the line, shunted by a back contact I) of the associated transmitter relay in order to equalize the response of the line relay to the signals delivered by the associated transmitter and to the one at the distant end 1;. of the line as is desirable when the attenuation of the line signals is high, and a low pass filter LP is interposed in the connection of the stations to line 4 to render the line available for voice or carrier current communication.

Another difference in Fig. 2 is the provision of a repeating relay T4 for the line relay R4 which controls the delivery of the carrier current codes to line 3 at the repeater station, in order to confine these currents to the contacts of a single relay.

It is to be understood that the line circuit system of Fig. 2 may be a portion of a through line circuit with the sections connected by suitable band pass filters BP, and may include a plurality of sections similar to line 4 each having a repeater station at one end for repeating the codes over the intervening line between that section and the ofiice by means of carrier currents as shown. each repeater and the associated ofiice apparatus employing a different frequency.

It is also to be understood that a series connectedline such as line 2 of Fig. 1. may replace the multiple connected line 3 in Fig. 2, or that sion of carrier currents over line wires as illus trated-by the line section 3,, and that two or more repeaters may be interposed in the circuit con-- necting the officeand stations of Fig. 1 r 2. The latter arrangement is illustrated more particularly in Fig. 3- in which a single frequency, twoway radio channel having the antennas A and Al as shown, provides a connection between two battery energized, multiple connected line circuits 3 and 4, Fig. 3 being in other respects similar-to: Fig. 2.

Considering the. operation of Fig, 3, it will be seen that when relay OT is operatedto deliver the. first. long impulse of a control codev to line 3, relays. R3, T3 L and, ILB. respond at the. first repeater stati0n,. rela T3- transmitting a radio. signal; of corresponding duration from antenna A which, is received; over antenna Al at. the sec- 0nd. repeater station to energize the, corresponding relays R311, Laand ILBa, and the receiving relay- R3asupplies. current from battery B to. line 4 over its front contact I). to cause relay R at each. field: station to; operate. its, coding unit CU in the manner already described in connection withFig, 1. a

When an indication code is initiated by the, system of Fig; 3, relay Tat the transmitting station. picks up and operates the associated relay Rand also. operates relay-RM at the second repeater station. Relay Rda completes a circuit from terminal B. atcontact b of relay ILBa over its; front contact b: to operate the repeating relay T4: which transmits a radio signal from antenna A]: is. received by antenna. A of the first repeater station to operaterelay- R4. The carrier current delivered to antenna AI also operates relay R3a locally. Relay R3a by closing its front contacts a and b energizes relays La and lLBa of the second repeater station and supplies current from' battery B4'to line 4 to, maintain relays, Rtaand- R,- energized. Contact I) of relay R4 at th first repeater stationnow closesto supply current from battery B3a to line 3 to operate relays R3 and: the oflice line relay OR. Relay R3 energizes relays T3, L and ILB at the first repeater station and relay T3 delivers carrier current from the associated oscillator OSC to antenna A, which alsoholdsrelay R4 energized.

At the second. repeater station relay T4 is released when relay lLBa' pickup and. opens. its back contact b and relay R30. is then held energized by the radio signal received over antenna AI from the first repeater stationand continues tosupply current from. battery B4' to line 4, under the control of relay R3, as. long as line 31 remains energized. When relay ILB at the first repeater station picks. up, its contact b disconnects battery 133a from line and its contact d connects relay R3. directly across line 3, and if relay OT has not been operated relays OR and R3 release, advancing the code supplied to line 3 to the second step, this occurring shortly before relay T releases to' advance the. code supplied to line 4 to the second step. Relay R3 releases relay T3, discontinuing the supply of carrier current to antenna A and releasing relay R4. Since: relays R3 and R4 are now both in the released position, relay ZLB picks up: and the opening of its contact 0. prevents further operation of relay T3, while the; operation ofv contact I) of relay 2LB to its upper position places line 3 under the control of contact I) of relay R4.

At the second repeating station relay RSa releases when the carrier. current received by antenna. Al is discontinued, to disconnect battery 134 from line l butrelays Rda and Rare held.

energized by current from battery B411 and release when relay T advances to-step two of the code. At the beginning of the second step of the code supplied to line 4, therefore, relays R and Rec release, relay ZLBa becoming energized. The operation of contact 0 of relay ZLBa prevents further control of line 4 by relay R3a and the operation of contact 17 of relay ZLBa establishes relay T4 as a repeater of relay T while relay ZLB, which is already energized, prevents further operation of relay T3 and conditions relay R3 to control relay OR through relay T4 by relay T, as in Fig. 1 already described.

The operation of push button PB in Fig. 3 during the transmission of an indication code by relay T likewise has the same result as in Fig. 1. When button ZPB is operated, relay R3 is steadily energized by battery B3 or B3a irrespective of the code operation of relay R4, causing relay ZLB to release and relay T3 to become steadily energized which in turn causes re- .lay Rita to be steadily energized to release relay ZLBa and to then supply steady current to line 4 to terminate the operation of the transmitting coding unit as-required.

Although I have hereinshown and described only a few forms of apparatus embodying my invention', it is understood that various. changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and. scope of my invention.

Having thus described my invention, what I claim is:

1. In a remote control system, an ofiice and a station connected by a single communication channel, code transmitters at the oflice and station for delivering impulse codes to said channel, a two-way repeater interposed in said channel, a slow acting relay and a stick relay associated with said repeater, means for energizing said slow acting relay in response to the first element of a code received at said repeater station, means controlled by said slow acting relay for selectively energizing said stick relay in accordance with the relative length of said first element, means controlled by said stick relay for establishing one direction or the other for the transmission of the remainder of the code through the repeater in accordance with the position of said stick relay, and. means responsive to said code for maintaining said stick relay picked up until said code is fully transmitted.

2. In a. remote control system, an office and a station, connected bya. single communication channel, code transmitters at the office and station for delivering impulse codes to said channel, a two-way repeater interposed in said channel including two stick relays and a slow acting relay, means for energizing one stick relay and said. slow acting relay in response to the first impulse of a code received at said repeater station, means controlled by said one stick relay for establishing one-way communicationthrough said repeater, means controlled by said slow acting relay for selectively energizing the other stick relay in accordance with the relative length of. said received impulse, means controlled by said other stick relay when energized for reversing the. direction of communication through said repeater. and. means controlled by the succeeding impulses of a code. for maintaining one or both of said stick relay-5. energized until such code is fully transmitted.

3. In. aremote control system, an office anda station, a first communication channel extending from the ofiice to a distant point, a second communication channel extending from said distant point to said station, coding units at the office and station each including a transmitter for delivering impulse codes to the adjacent channel and a receiver responsive to codes supplied thereto at said distant point, means causing the first impulse of a code delivered by the office transmitter to be of one character and the first impulse of a code delivered by the station transmitter to be of a different character, a two-way repeater at said distant point normally effective to repeat an impulse received from either channel into the other, means responsive to the first impulse of a received code for rendering said repeater effective to repeat succeeding impulses from the first channel to the second channel only, a stick relay associated with said repeater, means for energizing said stick relay following the reception of the first impulse of a code at the repeater station provided such impulse is of the character delivered by said station transmitter, means controlled by said stick relay when energized for reversing said repeater so as to repeat the succeeding impulses of a code from the second channel to the first channel only, and means for maintaining said stick relay energized until such code is fully transmitted.

4. In a remote control system, an office and a station, a first communication channel extending from the ofiice to a distant point, a second communication channel extending from said distant point to said station, coding units at the office and station each including a transmitter for delivering impulse codes to the adjacent channel and a receiver responsive to codes supplied thereto at said distant point, a two-way repeater at said distant point normally effective to repeat an impulse received from either channel into the other, means responsive to the first impulse of a code received over either channel for rendering said repeater effective to repeat impulses from the first channel to the second channel only, a stick relay associated with said repeater, means for energizing said stick relay following the reception of the first impulse of a code from said second channel provided no impulse is received from said first channel prior to the termination of said first impulse, means controlled by said stick relay when energized for reversingsaid repeater so as to repeat succeeding impulses received from the second channel to the first channel, and means for maintaining said stick relay energized only as long as the reception of such impulses continues.

5. In a remote control system, a two-way repeater connecting two communication circuits, comprising a line relay for each circuit, each such relay being responsive to code impulses received over its circuit from a distant transmitter and having a contact for repeating such impulses into the other communication circuit, means responsive to the first impulse of a code received from either of said circuits for locally terminating the corresponding impulse repeated into one of the two circuits before the received impulse is terminated, to thereby condition said repeater to repeat impulses in one direction only, from said one circuit into the other circuit, a stick relay, means,

for energizing said stick relay upon the termination of the first impulse of a code being received from the transmitter in said other circuit but only if no impulse is being received at the time from the transmitter in said one circuit, means controlled by said stick relay when energized for conditioning said repeater to repeat the remaining impulses of the code received from said other circuit into said one circuit, and means for maintaining said stick relay energized only until such code is fully transmitted.

6. In a remote control system, a two-way repeater connecting two communication circuits, comprising a line relay for each circuit, each line relay being adapted to repeat the impulses received over the corresponding circuit into the circuit which controls the other, two slow acting relays controlled by one of said line relays and arranged to be energized successively by such line relay when the first impulse of a code is received from either direction, means controlled by the first slow acting relay for opening the circuit for the second slow acting relay to effect its release during the first impulse received but only if such impulse is relatively long, means controlled by said first slow acting relay when energized for terminating the control of one of said line circuits by the line relay for the other to establish one-way transmission through said repeater, a stick relay controlled by the second slow acting relay, means efiective if the first impulse received is terminated before said second slow acting relay releases for energizing said stick relay, and means controlled by said stick relay when energized for reversing the direction of transmission through said repeater.

'7. In a remote control system, a two-way repeater connecting two communication circuits including a line relay for each circuit, each responsive to code impulses received over the corresponding circuit and normally adapted to repeat such impulses into the other circuit, two stick relays controlled by said line relays, a, pickup circuit for one stick relay closed when the first impulse of a code is received over either circuit, means effective upon the energization of said one stick relay for rendering the line relay controlled from said distant station ineffective to control the circuit extending to the ofiiice thereby establishing one-way communication from the oflice to the distant station through said repeater, a

pick-up circuit for the other stick relay closed only if no impulse is received from the oince during the reception of the first impulse .of a code from the distant station, and means effective when said second stick relay becomes energized for rendering the line relay controlled from said distant station effective to again control the circuit extending to the ofifice and for rendering the other line relay inefiective to control the other circuit, and a holding circuit for each stick relay including its own front contact and a; contact closed intermittently during the code operation of said line relays.

8. In a remote control system, a repeater including two line relays, a code transmitter at a control office for supplying code impulses to a first communication circuit extending to said repeater for controlling one of said line relays, a code transmitter at a distant station for supplying code impulses to a second communication circuit extending to said repeater for controlling the other line relay, means including contacts of said one line relay for repeating code impulses received from the oifice into said second circuit, means controlled by the other line relay in response to the first impulse of a code received from said station for locally generating an impulse of relatively brief duration and for supplying such impulse to said first circuit, and means efiective only if no impulse is received from the ofice durago-9,051

1'1 inglthe reception bysaid'repeater of the firstimpulse of a code received from said station for rendering the line relay for said second circuit efiective to repeat the succeeding impulses of such code into said first circuit.

9. In a remote control system, a repeater including two line relays, a code transmitter at a control office for supplying code impulses including a relatively long first impulse to :a first-communication channel extending to said repeater .for controlling one of said line relays, a code transmitter at a distant station for supplying code impulses including a relatively short first impulse to a second communication channel extending to said repeater forcontrolling the other line relay, code receivers at the office and station, means including contacts of said one line relay for repeating code impulses into said second channel to which the other line relay and the station receiver are responsive, means including contacts of the other line relay operated in responseto the short first impulse of a code received from the station for supplying a locally generated impulse of relatively brief duration to said first channel to which said one line relay and the oflice receiver are responsive, means selectively responsive to the long first impulse of a code received from the oifice for rendering the line relay controlled over said second channel inefiective to supply impulses to said first channel, and means effective upon the termination of the short first impulse of a code received from the station provided no impulse is received from the office during the reception of such impulse for rendering the contacts of the other line relay effective to repeat the succeeding impulses of such code into said first channel and for preventing said one line relay from repeating such impulses back into said second channel.

10. In a remote control system, a first and a second communication circuit connected by a repeater normally responsive to a code impulse received over either circuit for supplying an impulse to the other circuit, means in said repeater for terminating the impulse supplied to one circuit --pr-ior to the termination of the controlling impulse received from the other circuit, said repeater remaining efiective to repeat succeeding code impulses in the opposing direction only from said one circuit to said other circuit, and means efiective if no impulse is received from said one circuit during the reception of said impulse from the other circuit for reversing said direction to render the repeater effective to repeat succeeding impulses from-said other circuit -'to said-one-circuit only.

11. In a remote control system, an office and a station connected by a single communication channel, code transmitters at the oflice and station for delivering impulse codes to said channel, interference preventing means at the ofiice for determining the direction of code transmission over said channel in the event the transmission of codes is initiated at the cifice and station at approximately the same time, a two-way repeater interposed in said channel and normally efiective to repeat to said station a code impulse received from the office and to transmit an impulse of brief duration to said office in response to an impulse received from said station, said repeater then becoming effective to repeat impulses in one direction from the ofiice to the station only, and means effective if no impulse is received from the ofiice in response to the operation of said interefernce preventing means during the reception of an impulse from said station for reversing the direction of said repeater to render it eiTectiVe to repeat impulses from the station to the office only so long as the transmission of such impulses continues.

12. In a remote control system, an ofiice and a station connected by a single communication channel, code transmitters at the oflice and station for delivering impulse codes to said channel, a two-way repeater interposed in said channel nd normally effective to repeat to said station a code impulse received from the oifice and to transmit an impulse of brief duration to said office in response to an impulse received from said station, said repeater then becoming effective to repeat impulses in one direction from the ofiice to the station only, and means responsive to the first impulse of a code received from the station for reversing the direction of said repeater to render it efiective to repeat impulses from the station to the office only, said means being responsive to prolonged impulse received from the oflice during the transmission of any of said impulses including said first impulse for restoring said repeater to its original direction in which it is effective to repeat impulses from the ofiice to the station only.

LLOYD V. LEWIS. 

